/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.resource;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.lang.Nullable;
import org.springframework.util.AntPathMatcher;
import org.springframework.util.PathMatcher;
import org.springframework.util.StringUtils;
import org.springframework.web.servlet.handler.SimpleUrlHandlerMapping;
import org.springframework.web.util.UrlPathHelper;

/**
 * A central component to use to obtain the public URL path that clients should
 * use to access a static resource.
 *
 * <p>This class is aware of Spring MVC handler mappings used to serve static
 * resources and uses the {@code ResourceResolver} chains of the configured
 * {@code ResourceHttpRequestHandler}s to make its decisions.
 *
 * @author Rossen Stoyanchev
 * @since 4.1
 */
public class ResourceUrlProvider implements ApplicationListener<ContextRefreshedEvent> {

    protected final Log logger = LogFactory.getLog(getClass());
    private final Map<String, ResourceHttpRequestHandler> handlerMap = new LinkedHashMap<>();
    private UrlPathHelper urlPathHelper = new UrlPathHelper();
    private PathMatcher pathMatcher = new AntPathMatcher();
    private boolean autodetect = true;

    /**
     * Return the configured {@code UrlPathHelper}.
     *
     * @since 4.2.8
     */
    public UrlPathHelper getUrlPathHelper() {
        return this.urlPathHelper;
    }

    /**
     * Configure a {@code UrlPathHelper} to use in
     * {@link #getForRequestUrl(javax.servlet.http.HttpServletRequest, String)}
     * in order to derive the lookup path for a target request URL path.
     */
    public void setUrlPathHelper(UrlPathHelper urlPathHelper) {
        this.urlPathHelper = urlPathHelper;
    }

    /**
     * Return the configured {@code PathMatcher}.
     */
    public PathMatcher getPathMatcher() {
        return this.pathMatcher;
    }

    /**
     * Configure a {@code PathMatcher} to use when comparing target lookup path
     * against resource mappings.
     */
    public void setPathMatcher(PathMatcher pathMatcher) {
        this.pathMatcher = pathMatcher;
    }

    /**
     * Return the resource mappings, either manually configured or auto-detected
     * when the Spring {@code ApplicationContext} is refreshed.
     */
    public Map<String, ResourceHttpRequestHandler> getHandlerMap() {
        return this.handlerMap;
    }

    /**
     * Manually configure the resource mappings.
     * <p><strong>Note:</strong> by default resource mappings are auto-detected
     * from the Spring {@code ApplicationContext}. However if this property is
     * used, the auto-detection is turned off.
     */
    public void setHandlerMap(@Nullable Map<String, ResourceHttpRequestHandler> handlerMap) {
        if (handlerMap != null) {
            this.handlerMap.clear();
            this.handlerMap.putAll(handlerMap);
            this.autodetect = false;
        }
    }

    /**
     * Return {@code false} if resource mappings were manually configured,
     * {@code true} otherwise.
     */
    public boolean isAutodetect() {
        return this.autodetect;
    }

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        if (isAutodetect()) {
            this.handlerMap.clear();
            detectResourceHandlers(event.getApplicationContext());
            if (this.handlerMap.isEmpty() && logger.isDebugEnabled()) {
                logger.debug("No resource handling mappings found");
            }
            if (!this.handlerMap.isEmpty()) {
                this.autodetect = false;
            }
        }
    }


    protected void detectResourceHandlers(ApplicationContext appContext) {
        logger.debug("Looking for resource handler mappings");

        Map<String, SimpleUrlHandlerMapping> beans = appContext.getBeansOfType(SimpleUrlHandlerMapping.class);
        List<SimpleUrlHandlerMapping> mappings = new ArrayList<>(beans.values());
        AnnotationAwareOrderComparator.sort(mappings);

        for (SimpleUrlHandlerMapping mapping : mappings) {
            for (String pattern : mapping.getHandlerMap().keySet()) {
                Object handler = mapping.getHandlerMap().get(pattern);
                if (handler instanceof ResourceHttpRequestHandler) {
                    ResourceHttpRequestHandler resourceHandler = (ResourceHttpRequestHandler) handler;
                    if (logger.isDebugEnabled()) {
                        logger.debug("Found resource handler mapping: URL pattern=\"" + pattern + "\", " +
                                "locations=" + resourceHandler.getLocations() + ", " +
                                "resolvers=" + resourceHandler.getResourceResolvers());
                    }
                    this.handlerMap.put(pattern, resourceHandler);
                }
            }
        }
    }

    /**
     * A variation on {@link #getForLookupPath(String)} that accepts a full request
     * URL path (i.e. including context and servlet path) and returns the full request
     * URL path to expose for public use.
     *
     * @param request the current request
     * @param requestUrl the request URL path to resolve
     * @return the resolved public URL path, or {@code null} if unresolved
     */
    @Nullable
    public final String getForRequestUrl(HttpServletRequest request, String requestUrl) {
        if (logger.isTraceEnabled()) {
            logger.trace("Getting resource URL for request URL \"" + requestUrl + "\"");
        }
        int prefixIndex = getLookupPathIndex(request);
        int suffixIndex = getEndPathIndex(requestUrl);
        String prefix = requestUrl.substring(0, prefixIndex);
        String suffix = requestUrl.substring(suffixIndex);
        String lookupPath = requestUrl.substring(prefixIndex, suffixIndex);
        String resolvedLookupPath = getForLookupPath(lookupPath);
        return (resolvedLookupPath != null ? prefix + resolvedLookupPath + suffix : null);
    }

    private int getLookupPathIndex(HttpServletRequest request) {
        UrlPathHelper pathHelper = getUrlPathHelper();
        String requestUri = pathHelper.getRequestUri(request);
        String lookupPath = pathHelper.getLookupPathForRequest(request);
        return requestUri.indexOf(lookupPath);
    }

    private int getEndPathIndex(String lookupPath) {
        int suffixIndex = lookupPath.length();
        int queryIndex = lookupPath.indexOf("?");
        if (queryIndex > 0) {
            suffixIndex = queryIndex;
        }
        int hashIndex = lookupPath.indexOf("#");
        if (hashIndex > 0) {
            suffixIndex = Math.min(suffixIndex, hashIndex);
        }
        return suffixIndex;
    }

    /**
     * Compare the given path against configured resource handler mappings and
     * if a match is found use the {@code ResourceResolver} chain of the matched
     * {@code ResourceHttpRequestHandler} to resolve the URL path to expose for
     * public use.
     * <p>It is expected that the given path is what Spring MVC would use for
     * request mapping purposes, i.e. excluding context and servlet path portions.
     * <p>If several handler mappings match, the handler used will be the one
     * configured with the most specific pattern.
     *
     * @param lookupPath the lookup path to check
     * @return the resolved public URL path, or {@code null} if unresolved
     */
    @Nullable
    public final String getForLookupPath(String lookupPath) {

        // Clean duplicate slashes or pathWithinPattern won't match lookupPath
        String previous;
        do {
            previous = lookupPath;
            lookupPath = StringUtils.replace(lookupPath, "//", "/");
        } while (!lookupPath.equals(previous));

        if (logger.isTraceEnabled()) {
            logger.trace("Getting resource URL for lookup path \"" + lookupPath + "\"");
        }

        List<String> matchingPatterns = new ArrayList<>();
        for (String pattern : this.handlerMap.keySet()) {
            if (getPathMatcher().match(pattern, lookupPath)) {
                matchingPatterns.add(pattern);
            }
        }

        if (!matchingPatterns.isEmpty()) {
            Comparator<String> patternComparator = getPathMatcher().getPatternComparator(lookupPath);
            matchingPatterns.sort(patternComparator);
            for (String pattern : matchingPatterns) {
                String pathWithinMapping = getPathMatcher().extractPathWithinPattern(pattern, lookupPath);
                String pathMapping = lookupPath.substring(0, lookupPath.indexOf(pathWithinMapping));
                if (logger.isTraceEnabled()) {
                    logger.trace("Invoking ResourceResolverChain for URL pattern \"" + pattern + "\"");
                }
                ResourceHttpRequestHandler handler = this.handlerMap.get(pattern);
                ResourceResolverChain chain = new DefaultResourceResolverChain(handler.getResourceResolvers());
                String resolved = chain.resolveUrlPath(pathWithinMapping, handler.getLocations());
                if (resolved == null) {
                    continue;
                }
                if (logger.isTraceEnabled()) {
                    logger.trace("Resolved public resource URL path \"" + resolved + "\"");
                }
                return pathMapping + resolved;
            }
        }

        if (logger.isDebugEnabled()) {
            logger.debug("No matching resource mapping for lookup path \"" + lookupPath + "\"");
        }
        return null;
    }

}
